The objectives of the proposed research are to provide a description of the neural and photochemical events subserving visual adaptation in the vertebrate retina, to examine the role of the photoreceptors in the adaptation process, and to elucidate the mechanisms by which information is transferred from the receptors to the more proximal neurons. The visual pigments and their photosensitive reactions will be studied in situ using the methods of transmission spectrophotometry and fundus reflectometry. Emphasis will be placed on examining the effects of light and dark adaptation, temperature variation, calcium and other ionic species on photopigment kinetics and the concomitant changes in electrical responses of photoreceptors. Intra-cellular recordings from horizontal and bipolar cells will be used to test the efficacy of various putative transmitters and their analogues on membrane potentials and light-evoked responses in order to identify the chemical mediators of signal transmission in the distal retina.